The present invention relates to a method for controlling the torque transmitting ability of a transmission arranged between a crankshaft of an turbocompound combustion engine and a power turbine of said turbocompound combustion engine.
In particular, the invention will find its application in connection with automotive vehicles, and relates to a method for improved control of said transmission. The invention also relates to a computer program, when run on a computer, computer program product and a storage medium, such as a computer memory.
A turbocompound combustion engine, such as disclosed in for example U.S. Pat. No. 5,884,482, is equipped with a turbocharger turbine arranged for receiving exhaust gas from said combustion engine. Such a turbocompound combustion engine is further equipped with a power turbine arranged for receiving said exhaust gas from said turbocharger turbine. Pressure force from the exhaust gases is transmitted to a crank shaft of the engine via a transmission to be used for vehicle propulsion. Said transmission driven by the power turbine and connected to the crankshaft comprises a hydrodynamic coupling. The hydrodynamic coupling is used in order to avoid transmission of damaging irregular rotation to the power turbine and gearing on the power turbine side of the hydrodynamic coupling. The irregular rotation is the result of the combustions occurring in the different cylinders of the engine during a relatively very short period of time of a turn of the crank shaft. A combustion creates a sudden temporary rotational acceleration of the crank shaft, which has negative exhaustive effect on mechanical parts of the engine. Said hydrodynamic coupling reduces the transmission of said negative effect.
When the combustion engine is turned off and said hydrodynamic coupling is in its off-state and not rotating, part of the coupling can never be fully drained from fluid (oil). This means that when the combustion engine is started and the exhaust pressure in the exhaust pipe has not yet been built up in order to be able to drive the power turbine, the combustion engine will experience an extra resistance in rotation due to the partly filled hydrodynamic coupling transmitting moment of inertia from the inertia of the non-rotating power turbine and the belonging gearing on the power turbine side of the hydrodynamic coupling. Said extra resistance is hard to control and the performance of the combustion engine just after start can be uncertain.
US20040068986 and US2007275820 both disclose a turbocompound arrangement, where a braking device is arranged for braking a power turbine side of a hydrodynamic coupling. US2007275820 mentions that the hydrodynamic coupling can be operated with a partial filling in a braking operation in order to adjust the optimal braking power. Further, here is a cooling device of the hydrodynamic coupling integrated with a combustion engine cooling device. This can be used for transporting heat from the hydrodynamic coupling to the combustion engine at, for example, cold starts.
A technical problem addressed by the present invention is how to provide a more advanced transmission between the power turbine and the crank shaft, which will be able to offer an increased overall combustion engine control.
It is desirable to provide an improved transmission between the power turbine and the crank shaft that will increase the controllability of the hydrodynamic coupling and the power turbine.
Moreover, it is desirable to provide increased control of the transmission between the power turbine and the crank shaft in order to increase the overall performance of the engine, especially for lowering noise and exhaust emissions from the engine, and accelerated heating of the combustion engine during cold starts but also for a better auxiliary braking performance.
Thus, it is desirable to solve the above problems and to provide an improved method for controlling said transmission.
The method according to an aspect of the invention is a method for automatically adjusting torque transmitting ability of a transmission arranged between a power turbine and a crank shaft in a turbocompound combustion engine, said transmission comprising a hydrodynamic coupling, and said method comprising the steps of:
continuously registering a value for one or several of;
a. engine load parameter for said combustion engine and/or,
b. temperature in said combustion engine and/or,
c. parameters for indicating NVH (noise vibration harshness) in said transmission;
if one or several of parameters a to c has passed a predetermined value for each of said parameters in one first direction, then braking a power turbine side of said hydrodynamic coupling and continuously adjusting said torque transmitting ability of said hydrodynamic coupling in dependence of the development of one or several of said parameters a to c.
In one embodiment according to an aspect of the invention said method is characterized in braking said power turbine side of the hydrodynamic coupling to at least a rotational speed below a rotational speed of a turbocompound combustion engine side of the hydrodynamic coupling. In one further embodiment said power turbine side is braked to zero rotational speed.
In a further embodiment according to an aspect of the invention said method is characterized in that continuously adjusting said torque transmitting ability in such a way and until a registered value for each of said one or several parameters a to c has returned back and passed said predetermined value in an opposite direction compared to said first direction.
In another embodiment according to an aspect of the invention said method is characterized in that releasing said braking device when a registered value for each of said one or several parameters a to c has returned back and passed said predetermined value in an opposite direction compared to said first direction.
The invention also relates, in an aspect thereof, to a computer program comprising program code means for performing all the steps of any one of the method claims when said program is run on a computer.
The invention also relates, in an aspect thereof, to a computer program product comprising program code means stored on a computer readable medium for performing all steps of anyone of the method claims when said program product is run on a computer.
The invention also relates, in an aspect thereof to a storage medium, such as a computer memory or a nonvolatile data storage medium, for use in a computing environment, the memory comprising a computer readable program code to perform the method of method claim.